Background and objective: Optic neuritis (ON) is associated with a 38% ten-year risk of developing multiple sclerosis (MS) in Western populations, but the corresponding risk in non-Western populations is unclear. We conducted this study to estimate the risk of progression to MS after an episode of ON in a South Asian population. Methods:Two hundred and fifty-three Patients with idiopathic ON were identified by reviewing records of visual evoked potentials and chart notes from a single academic center spanning the years 1990-2007. A structured telephone interview was then conducted to identify Patients who had subsequently received a diagnosis of MS. The diagnosis was corroborated from chart notes, where possible. Cumulative probability of conversion to MS was calculated using Kaplan-Meier survival analysis.

Results:

The five-year risk of developing MS was 14.6% and the ten-year risk was 24%. Patients (N=218) who had one or more typical demyelinating lesions on baseline brain magnetic resonance imaging (MRI) had a 68% 10-year risk, those with no lesions or non-typical lesions had a 14% risk (pConclusion: Idiopathic ON in Pakistan carries a lower risk of progression to MS compared with Western data. As in Western populations, however, presence of abnormal baseline brain MRI and CSF oligoclonal bands correlate with increased MS risk.